Experimental allergic encephalomyelitis (EAE) is induced in susceptible animals by immunodominant determinants of myelin basic protein (MBP), such as guinea pig sequence MBP72-85. Two linear and one cyclic analogues based on MBP72-85 have been synthesized and evaluated for EAE induction in Lewis rats. The linear peptide Gln1-Lys2-Ser3-Gln4-Arg5-Ser6-Gln7-+ ++Asp8-Glu9-Asn10-Pro11-Val12 (1) was found to induce EAE, while substitution of the Asp residue at position 8 with Ala resulted in an analogue (2) which suppressed the induction of EAE by its parent peptide. Nuclear magnetic resonance studies of analogue 1 in dimethyl sulfoxide (DMSO) using TOCSY/ROESY techniques revealed a head-to-tail intramolecular interaction (ROE connectivity between betaVal12-gammaGln1), indicating a pseudocyclic conformation for the immunogenic peptide 1. A conformational model was developed using NMR constraints and molecular dynamics. Based on this model, a novel amide-linked cyclic analogue has been designed and synthesized by connecting the side-chain amino and carboxyl groups of Lys and Glu at positions 2 and 9, respectively, of linear analogue 1. The cyclic analogue (3) had similar activity to the linear peptide 1, and the EAE effects induced by cyclic analogue 3 were completely suppressed by co-injection with the Ala81-substituted analogue 2 in Lewis rats. The similar potencies of analogues 1 and 3 support the proposed cyclic comformation suggested for analogue 1 from NMR studies and computer modeling and provides the basis for designing more potent molecules with improved properties such as increased resistance to degradation.15 The present findings suggest that a cyclic conformation for the MBP72-85 epitope positions the carboxyl group of Asp81 correctly and presumably other side groups of the peptide such as Arg78 in a manner which enables functional binding of the trimolecular complex MHC-peptide-T cell receptor resulting in EAE.